Major elements and lithostratigraphic study of the contact rocks of the Togo and the Dahomeyan formations in Ghana

Abstract

The thrust contact between the Togo and the Dahomeyan formations in Ghana is a lithotectonic boundary that exists between two major Precambrian formations which are of importance to geologists owing to the fact that Precambrian rocks in Ghana host almost all economic minerals and metals. The lithostratigraphy of the Togo-Dahomyan thrust contact rocks from a borehole in Kwabenya near Accra (the Capital of Ghana) has been studied and major crustal chemical elements assayed using Instrumental Neutron Activation Analysis (INAA) techniques. The results have revealed elemental compositions and the mineralogical make up of the lithostratigraphic units of these contact rocks and the general geology of the Togo and the Dahomeyan formations. The profile shows a thrust contact that exists between the Togo formations which are underlying the Dahomeyan formations. The Togo formations here are made mainly of quartzite in fresh schist and the Dahomeyan made of gneisses. In between these two major geologic formations are the rocks of the contact which are intercalation of quartzite and schist. The rocks are felsic with an average felsic index (F) of 85.74 and feldspar rich with K- (orthoclase) feldspars dominating the Dahomeyan rocks. Iron and titanium oxides are depleted with depth from 52 m depth below surface downward and potassium oxide was enriched with depth from 42 m below surface downward. Major mineral forming elements such as aluminum and calcium had varied levels in the Togo and in the Dahomeyan rocks.